The present invention is directed to communication receivers and, more particularly, to blind rate determination in communication receivers.
Digital communication systems typically include a mobile unit, which may be embodied in a digital cellular telephone or any other portable communication device, and an infrastructure unit, which may be embodied in a cellular base station or any other suitable communication hardware. During operation, the mobile unit and the infrastructure unit exchange digital information using one of a number of communication protocols. For example, the mobile and infrastructure units may exchange information according to a time division multiple access (TDMA) protocol or a code division multiple access (CDMA) protocol. The details of such protocols are disclosed in the IS-136 and IS-95 communication standards, which are available from the Telecommunication Industry Association (TIA).
Mobile and infrastructure units broadcast information at various rates in the CDMA system. For example, data rates in a CDMA system may vary between 1.2 and 9.6 kilobits per second (kbps). In accordance with the IS-95 specification, receivers in the mobile and infrastructure units do not have a priori knowledge of the data rate of the information that they are about to receive. Accordingly, CDMA receivers must blindly determine the rate at which they are receiving data.
One technique of blind rate determination disclosed in U.S. Pat. No. 5,796,757 to Czaja includes decoding a received signal and determining, for each possible data rate, a total cumulative metric associated with a most likely path through a decoder trellis. The total cumulative metric is determined by, among other things, processing branch metrics to determine survivor metrics, which requires the received signal to be decoded for each possible data rate.
Another blind rate determination technique disclosed in U.S. Pat. No. 6,112,325 to Burshtein includes the use of specific quality metrics to determine the rate at which a digital receiver receives information. In particular Burshtein discloses that the quality metrics may be a rate at which a function of signal to noise is optimized or the quality metrics may be cyclic redundancy check errors.
An additional blind rate determination technique includes Viterbi decoding a received signal for each of the possible data rates, convolutionally encoding the decoded signals and comparing the results of the convolutional encoding with the received signal. Typically, such a comparison is a straight bit-wise comparison that looks for the minimum bit error rate and adopts the rate associated with the minimum bit error rate. While this is a good approximation for deciding the rate at which the data was sent, the results of a bit-wise comparison are simply positive or negative indications of matches. Such an approach does not use soft decision or confidence information to make a rate determination. Further, problems may be encountered when a very low data rate is used because there are fewer bits per frame over which the bit-wise comparison may be taken. For example, a 20 millisecond (ms), 384 bit frame encoded with a 1.2 kbps data rate may contain only 16 bits of meaningful information over which bit wise comparisons may be made. Additionally, some bits in a frame may be used as power control bits to provide a mobile unit information on whether the mobile unit should increase or decrease its transmit power level to optimize the transmit level of the mobile unit relative to the environment. Typically, for rate determination purposes, the power control bits are all set to zero. Accordingly, fewer bits are available to compare when power control bits are used, which further reduces the reliability of rate determination based on bit error rate.
According to one aspect, the present invention may be embodied in a method of determining a data rate at which data is encoded within a digital signal. The method may include selecting an assumed data rate at which data may be encoded within the digital signal, determining a syndrome of the digital signal for the assumed data rate and determining a confidence metric related to the syndrome of the digital signal. The method may also include comparing the confidence metric to a threshold and producing an indication that the assumed data rate is the data rate at which data is encoded within the digital signal if the confidence metric satisfies the threshold.
According to a second aspect, the present invention may be embodied in a method of determining a data rate at which data is encoded within a digital signal. The method may include selecting a plurality of assumed data rates at which data may be encoded within the digital signal, determining a plurality of syndromes of the digital signal, wherein each one of the plurality of syndromes is related to each one of the plurality of assumed data rates and determining a plurality of confidence metrics, wherein each one of the plurality of confidence metrics is related to each one of the plurality of syndromes. Additionally, the method may include determining a best confidence metric of the plurality of confidence metrics, wherein the best confidence metric has a related assumed data rate, comparing the best confidence metric to a threshold and producing an indication that the assumed data rate related to the best confidence metric is the data rate at which data is encoded within the digital signal if the best confidence metric satisfies the threshold.
According to a third aspect, the present invention may be embodied in a system adapted to determine a data rate at which data is encoded within a digital signal. The system may include a derepeater adapted to process the digital signal according to an assumed data rate at which data may be encoded within the digital signal, a syndrome determiner coupled to the derepeater and adapted to determine a syndrome of the digital signal for the assumed data rate and to determine a confidence metric related to the syndrome of the digital signal and a comparator coupled to the syndrome determiner and adapted to compare the confidence metric to a threshold and to produce an indication that the assumed data rate is the data rate at which data is encoded within the digital signal if the confidence metric satisfies the threshold.
According to a fourth aspect, the present invention may be embodied in a system adapted to determine a data rate at which data is encoded within a digital signal. The system may include a derepeater adapted to process the digital signal according to a plurality of assumed data rates at which data may be encoded within the digital signal and a confidence metric determiner coupled to the derepeater and adapted to determine a plurality of syndromes of the digital signal, wherein the syndrome determiner is adapted to determine a plurality of confidence metrics based on the plurality of syndromes. The system may also include a comparator coupled to the confidence metric determiner and adapted to determine a best confidence metric of the plurality of confidence metrics, to compare the best confidence metric to a threshold and to produce an indication that the assumed data rate related to the best confidence metric is the rate at which data is encoded within the digital signal if the best confidence metric satisfies the threshold.
According to a fifth aspect, the present invention may be embodied in a rate determiner for use in a receiver including a processor, wherein the rate determiner is adapted to determine a data rate at which data is encoded within a digital signal. The rate determiner may include a memory, a first set of instructions stored on the memory and adapted to cause the processor to select an assumed data rate at which data may be encoded within the digital signal and a second set of instructions stored on the memory and adapted to cause the processor to determine a syndrome of the digital signal for the assumed data rate. The rate determiner may also include a third set of instructions stored on the memory and adapted to cause the processor to determine a confidence metric related to the syndrome of the digital signal, a fourth set of instructions stored on the memory and adapted to cause the processor to compare the confidence metric to a threshold and a fifth set of instructions stored on the memory and adapted to cause the processor to produce an indication that the assumed data rate is the data rate at which data is encoded within the digital signal if the confidence metric satisfies the threshold.
According to a sixth aspect, the present invention may be embodied in a rate determiner for use in a receiver including a processor, wherein the rate determiner is adapted to determine a rate at which data is encoded within a digital signal. In such an embodiment, the rate determiner may include a memory, a first set of instructions stored on the memory and adapted to cause the processor to select a plurality of assumed data rates at which data may be encoded within the digital signal and a second set of instructions stored on the memory and adapted to cause the processor to determine a plurality of syndromes of the digital signal related to the assumed data rates. The rate determiner may also include a third set of instructions stored on the memory and adapted to cause the processor to determine a plurality of confidence metrics, wherein each one of the plurality of confidence metrics is related to the plurality of syndromes and a fourth set of instructions stored on the memory and adapted to cause the processor to determine a best confidence metric of the plurality of confidence metrics, wherein the best confidence metric has a related assumed data rate. Further, the rate determiner may include a fifth set of instructions stored on the memory and adapted to cause the processor to compare the best confidence metric to a threshold and a sixth set of instructions stored on the memory and adapted to cause the processor to produce an indication that the assumed data rate related to the best confidence metric is the data rate at which data is encoded within the digital signal if the best confidence metric satisfies the threshold.
These and other features of the present invention will be apparent to those of ordinary skill in the art in view of the description of the preferred embodiments, which is made with reference to the drawings, a brief description of which is provided below.